Both vitamins A and D are fat-soluble and essential vitamins in the
diets of dogs and cats.

Vitamin A is important for normal vision, immune function, fetal development, growth, and cellular differentiation (important for
maintaining healthy skin cells, corneal cells, and other cells
lining the respiratory, gastrointestinal, and reproductive tracts)12.

Vitamin D plays a major role in maintaining normal body calcium levels
and facilitating calcium absorption from the gastrointestinal tract. Unlike humans, dogs and cats have an essential dietary requirement for
vitamin D due to an inability to adequately form vitamin D in the skin. Vitamin D deficiency is characterized by an inadequate mineralization
of the bone and growth plates, also know as rickets12. 12. Nutrient Requirements of Dogs and Cats. National Research Council of the National Academies. The National Academies Press, Washington, DC, 2006.